This invention relates to electro-optical modulators, and more particularly to improved waveguide coupling in such devices.
The modulation of light beams, particularly coherent light such as produced by a laser, has been accomplished through the use of electro-optic modulators wherein a varying voltage is used as the modulating signal. Such modulators are exemplified by U.S. Pat. Nos. 3,506,929 to A. A. Ballman, et al., and 3,656,836 to B. de Cremoux et al. As shown in the Ballman patent, a light transmitting substrate or wave guide formed of lithium tantalate (Li Ta O.sub.3) crystal has electro-optic characteristics that effectively modulate light when subjected to an electrical field developed between electrodes carried by the substrate. In the manufacture of practical electro-optic modulators for laser beams, efficiency of coupling of light into and out of the wave guide substrate becomes important. One approach has been to use reflective gratings ruled in the wave guide surface to alter the light beam path. Small sizes of elements and critical entrance angles, however, make alignment procedures between the light source and the crystal substrate difficult and expensive. Moreover, the prior grating coupled modulators have not permitted the insertion of the modulator directly on line in a system. Accordingly, it would be desirable to provide an improved electro-optical modulator wherein alignment between the source and the substrate is not as critical as has been experienced heretofore, and which will permit direct "on line" incorporation in a system.